To date, we know of no examples of American Revolutionary War fifes that have been substantiated, and any claim of one for sale on the internet should immediately be considered suspect. Surprisingly, most antiques dealers are not qualified to identify these instruments properly. So without archaeological evidence (with supporting physical charactaristics) that places the instrument in a specific place and time, most claims are really just guesses.
We know of two instruments that claim Revolutionary vintage, but these have so far been proven to be 19th century examples. One is a fife in a Lexington house museum made by William Callender, who wasn't listed in the Boston city directories until 1796 (and not as a fife maker until 1802) and another is an iron fife at the Smithsonian, claimed to have been made from a musket barrel but made, according to a letter from the curator of musical instruments, during the Centennial celebrations and not during the War itself. There is a third candidate at Saratoga, also of iron, that we have yet to inspect, and someone on the Rev. War email list mentions a fourth but will not give further information. Again, it too remains suspect since it can't be examined.
We do have some pretty reliable information about one specific fife from the War of 1812 made by Heinrich Eisenbrandt, a German immigrant who made fifes in Philadelphia. He was unusual for a couple of reasons. First, he developed a technique for drilling fife bores in one step (his competitors did this in several steps, thus taking a longer period of time) that enabled him to turn out many fifes in a shorter period of time for less money, something that won him large government contracts during the War of 1812. Second, he shunned boxwood, the wood of choice for legitimate woodwind makers, in favor of rosewood, and he was the only one to do so at this early date. So his fifes are fairly easy to identify.
On the British side, there is not much more available. One of our members has a Valentine Metzler fife, a beautiful boxwood example, that could have been made as early as 1785 or as late as 1814.
Both the Eisenbrandt and the Metzler fifes are good examples of "early" instruments from their respective countries, and unfortunately those are the earliest examples we have. We do know that in America there is evidence (newspaper ads, for one) for fifes being made in woodwind shops as well as by craftsmen in other trades, such as clockmaking and cabinetmaking. These fifes tend to be made of boxwood. There is equal evidence, this time in surviving examples, of fifes produced in backyard barns and workshops. These in turn prove to be of domestic woods--maple and fruitwoods being the most common. Since these fifes are never marked with a maker's name or mark, there is really no way of determining their age except by construction characteristics (tonehole size and placement, ferrule design, etc), and then it's only a ballpark figure.